Like you said indeed you should be able to run the game on at least 5 machines at the same time.
You should try to revoke the licence on the first computer, check activation.exe in order to see if you have 5 activations left.
Then install the Game on the computer B and try on computer A to see if you are still getting the same message.
If your issue persists, please contact a Game Advisor by clicking here.
Also for more information, you can have a look at the Solidshield activation and revocation article [Link to the Solidshield website.]
